Porphyrins dimeric

Plots of the CD intensity of 23 (1.00 x 10 M) at 405 nm versus [Mj. The solid lines represent the theoretical curves for the formation of the [23-(M )2] complex. Mj glucose, Mj maltose, M3 maltotriose, M4 maltotetraose, M5 maltopentaose. Reproduced with permission from ref. 27. 2000 John Wiley Sons. 

Arimori et al utilized the electrostatic interaction to generate dimeric boronic acid-appended porphyrins. Anionic porphyrin 25 and cationic porphyrins 16 form 1 1 complexes, which give the specific exci ton-coupling bands in CD spectroscopy only in the presence of glucose and xylose. The CD sign is characteristic for the absolute configuration of the saccharides. Structural examination established that only these monosaccharides can bridge two porphyrins by ester formation with boronic acid and twist them asymmetrically. 

---

The coupling reaction of zinc(II) (3- or)8-monobromodeuteroporphyrin dimethyl ester (ID with 1,4-divinylbenzene under the typical conditions of the Heck reaction results in the formation of dimeric porphyrin 12 linked via a divinylbenzene moiety. Use of 1,3,5-trivinyl-benzene in the same reaction makes the trisadduct available."5... 

Interpreting these results on a detailed molecular basis is difficult because we have at present no direct structural data proving the nature of the split Co(IIl/lI) voltammetry (which seems critical to the electrocatalytic efficacy). Experiments on the dissolved monomeric porphyrin, in CH-C solvent, reveal a strong tendency for association, especially for the tetra(o-aminophenyl)porphyrin. From this observation, we have speculated (3) that the split Co(III/II) wave may represent reactivity of non-associated (dimer ) and associated forms of the cobalt tetra(o-aminophenyl)porphyrins, and that these states play different roles in the dioxygen reduction chemistry. That dimeric cobalt porphyrins in particular can yield more efficient four electron dioxygen reduction pathways is well known (24). Our results suggest that efforts to incorporate more structurally well defined dimeric porphyrins into polymer films may be a worthwhile line of future research. 

A wide range of dimeric porphyrins have been synthesized with specific objectives. Recent examples include face-to-face dimers in which the porphyrins are linked by bridges located at... 

Kimura, Shirai and coworkers used two chiral dimeric porphyrins 95 and 96 to investigate their self-assembling behavior [162,163]. While incorporation into fibers made of the alkylamide derivatives of (fl,fl)-DACH, 95 formed stable well-resolved fibrous assemblies as visualized by transmission electron microscopy, the fluorescence of which was not quenched by external electron acceptors [162]. However, the induced CD was not detected indicating an inability of 95 to form chirally orientated aggregates under the applied conditions. In contrast, 96 was able to produce optically active inter molecular self-assemblies with an enhanced chiroptical response through the //-oxo bridging in an alkali solution, while intramolecular //-oxo dimer formation was excluded on the basis of steric reasons [163]. 

Dubowchik, G. and Hamilton, A.D. 1985. Controlled conformational changes in covalently-linked dimeric porphyrins, J. Chem. Soc., Chem Commun., 904-906. 

A number of dimetallic face to face dimeric porphyrins containing Mn11 have been synthesized.505 For example, urea-linked TPP dimers (191) have been obtained containing imidazolate ligands... 

A range of heteronuclear metal-metal bonded dimeric porphyrin complexes have also been prepared. ... 

Figure 11 Structure of Mu2-dimeric porphyrin complex (1) and a reaction pathway for O2 formation through a dunanganyl (V,V) species (2)...

Hunter. C.A. Sarson, L.D. Self-assembly of a dimeric porphyrin host. Angew. Chem.. Int. Ed. Engl. 1994, 33. 2313. 

Hereafter the values of AG A// and A5 refer to the standard state of 1 M of each species. We also use notation, A-B, to represent a host-guest complex between compound A and compound B. Table I summarizes the binding free energy for complex formation for various amine-metallo-porphyrin complexes. Monomeric porphyrins bind amines with — AG values in the range of 10-25 kJ/mol, while dimeric porphyrins bind ditopic guests with a larger — AG of 30-43 kJ/mol. 

Boijesson K, WoUer JG, Parsa E, Martensson J, Albinsson B. A bioinspired self assembled dimeric porphyrin pocket that binds electron accepting ligands. Chem Comm. 2012 48 1793-1795. 

Scheme 30 Yorimitsu and Osaka s synthesis of new dimeric porphyrins.

Among the various approaches for porphyrin dimers, porphyrins having a crown ether moiety within the molecule have shown intraesting dimer formation through complexation with cations such as and Ca. Diffaent types of dimer... 

A slipped cofacial dimer porphyrin was reported that the substituent coordinated to Zn metal of another porphyrin [696]. A strong coupling was observed in that case (14). Metallochloiin was also reported to form multilayered slipped cofacial aggregates [699] (Fig. 44). 

The electron transport from dimer porphyrin to the terminal pyromellitdii-mide or quinone afford the ion pair with a lifetime in the order of is (32,33) [569,570] and long lifetime of 16 ps in THF (34) [574]. Obviously, the lifetimes of ion pairs were roughly in the order of diad < triad < tetrad < pentad systems. Other approaches such as proton coupling to the electron transfer [576] as observed in photosynthesis [575], enhancement of electron transfer by pyridine coordination to the central metal [577], and linked molecular systems having oligomeric porphyrins [572-574], carotenoide [543,582-589], aromatic molecules [590-594,753,754], cleft-type [789], [578-581], and Q, [477,595-599,... 

In 1996, the research groups of Osuka and Mataga reported the multistep electron transfer process in the Zn-porphyrin dimer-porphyrin-phyromellitimide system. In this system, initial charge separation occurred only between the Zn-porphyrin dimer and porphyrin like in the natural photosynthesis system. Then, the photogenerated electron shifted to pyromellitimide. The lifetime and yield of the final charge-separated state were estimated to be 290 ns and >0.8 respectively. 

---